The ability to precisely target and position single particles has numerous applications including particle-by-particle assembly of larger microstructures as well as probing and manipulation of tissues, groups of cells and single cells. There is a growing need for simple, cost-effective and robust systems that can manipulate single micro-particles in many scientific fields ranging from micro/nanotechnology to biology. Most existing particle manipulation or gripping systems found in literature require relatively expensive and complicated fabrication and instrumentation steps that significantly reduce the robustness and reproducibility in operation. Hence, many of these systems have not enjoyed wide acceptance.
Researchers have developed gripping systems that are based on piezoelectric effect to produce elastic deformation of a structure upon the application of sufficient voltage. See e.g., Basrour, S., Robert, L., 1997, “Mechanical characterization of micro-grippers realized by LIGA technique,” 1997 International Conference on Solid-state Sensors and Actuators, Vol. 1, pp. 599-602; Tan, K. K., Ng, S. C., 2001, “Computer controlled piezo micromanipulation system for biomedical applications,” Engineering and science journal, Vol. 10, pp. 249-256; Eisinberg, A., Houston, K., Caparrelli, P., Amavasai, B., Boissenin, M., 2006, “Marking techniques for vision recognition of microgrippers for micromanipulation,” Proceedings of the 2006 IEEE International Conference on Robotics and Automation, pp. 1030-1035; Ferreira, A., Agnus, J., Chaillet, N., Breguet, J., 2004, “A Smart Microrobot on Chip: Design, Identification, and Control,” IEEE/ASME Transactions on Mechatronics, Vol. 9, No. 3; Agnus, J., Nectoux, P., Chaillet, N., 2005, “Overview of Micro-grippers and Design of a Micromanipulation Station Based on a MMOC Micro-gripper,” Proceedings 2005 IEEE International Symposium on Computational Intelligence in Robotics and Automation, pp. 117-123; Grossard, M., Rotinat-Libersa, C., Chaillet, N., 2007, “Redesign of the MMOC microgripper piezoactuator using a new topological optimization method,” 2007 IEEE/ASME International conference on advanced intelligent mechatronics, pp. 1-6; and Bliderana, M. M., Fleischera, M., Grauvogelb, F., Löfflerb, K., Langerb, M. G., Kerna, D. P., 2008, “Real-time gripping detection for a mechanically actuated microgripper,” Microelectronic Engineering In Press 2008.
For example, Jericho et al. developed a piezoelectric MEMS micro-tweezers for the manipulation of micro-objects. See, Jericho, S. K., Jericho, M. H., 2004, “Micro-electra-mechanical systems micro-tweezers for the manipulation of bacteria and small particles,” Review of Scientific Instruments, Vol. 75, No. 5. As shown in FIG. 1a, the gripping parts of this tweezers consist of short bars with a cross-section of 2 μm×2 μm. The tweezers tips have a 15 μm rest opening and require about 70V for full closing. Since voltage control on the order of 1 to 2 volts is easily achieved, clamping forces as low as a few hundred nano-newtons can be obtained. The tweezers are activated by a 2 μm×2 mm long polysilicon bar that is coupled to a piezoelectric strip actuator by a thin aluminum rod.
Henein et al. present a high precision flexible micro-tweezers designed for micro-objects, as depicted in FIG. 1b. See, Henein, S., 2001, “Flexible Micro-Gripper for Micro-Factory Robots,” Conception des guidages flexibles, Presses Polytechniques et Universitaires Romandes. The piezoelectric effect is used to actuate flexure hinges which produce symmetric parallel movement of the gripping jaws. The device is fabricated using Electro-Discharge Machining (EDM). Piezo-resistive force sensors are used to measure the force being imparted on the object manipulated.
Carrozzay et al. disclose a lithography fabricated micro-tweezers, as shown in FIG. 1c. See, Carrozzay, M C., Menciassi, A., Tiezzi, G., Dario, P., 1998, “The development of a LIGA-microfabricated gripper for micromanipulation tasks,” Journal of Micromechanics and Microengineering, Vol. 8, No. 2. The device works by the application of piezoelectric actuating force to the external thin beams while the internal beams are rigidly constrained to produce rotation and translation at the tips of the tweezers to close them.
Park et al. developed a gripping device with the three chop stick design shown in FIG. 1d. See, Park, J., Moon, W., 2005, “The systematic design and fabrication of a three-chopstick microgripper,” International Journal of Advanced Manufacturing Technology, Vol. 26, pp. 251-261. Two of the sticks grip the micro-object while the third is used for hold and release functions. The stack and bender actuators are both piezoelectric actuators. The piezoelectric bender is used to actuate the two outside prongs, while the middle prong is actuated by the piezoelectric stack in the opposite direction to the other two. The chop sticks are made out of tungsten using Electro-Discharge Machining and precision micro-assembly. This device is intended for objects about 100 μm in size; hence the gap between the fingers is also 100 μm.
Most commonly used piezoelectric actuators usually need high activation voltages of around 60-70V. Since they can only produce a few microns of displacement, multilayers of actuators or multiple actuators are needed. This significantly increases the complexity of the microfabrication process, which results in devices that are expensive and hard to reproduce (both in terms of fabrication and operation).
Researchers have also explored the use of thermal actuation within gripping devices. See Honnatti, M., Hughes, G., “Directed Cellular Manipulation Using Polymer Microgrippers,” Zyvex Instruments; Bordatchev, E. V., Nikumb, S. K., 2005, “Electro-thermally driven microgrippers for microelectro-mechanical systems applications,” Journal of Microlithography, Microfabrication, Microsystems. Vol. 4; Suzuki, Y., 1994, “Fabrication and evaluation of flexible microgripper,” Japan Journal of Applied Physics. Vol. 33, pp. 2107-2112; Molhave, K., Hansen, O., 2005, “Electro-thermally actuated microgrippers with integrated force-feedback.” Journal of Micromechanics and Microengineering. Vol. 15, pp. 1265-1270; Du, H., Su, C., Lim, M. K, Jin, W. L., 1999, “A micromachined thermally-driven gripper: a numerical and experimental study,” Smart Materials and Structures. Vol. 8, pp. 616-622; Volland, B. E., Ivanova, K., Ivanov, T., Sarov, Y., Guliyev, E., Persaud, A., Zöllner, J. P., Klett, S., Kostic, I., Rangelow, I. W., 2007, “Duo-action electro thermal micro gripper,” Proceedings of the 32nd International Conference on Micro- and Nano-Engineering. Vol. 84, pp. 1329-1332; Andersen, K. N., Carlson, K., Petersen, D. H., Mølhave, K., Eichhorn, V., Fatikow, S., Bøggild, P., 2008, “Electrothermal microgrippers for pick-and-place operations,” Microelectronic Engineering In Press 2008; Fraser, J., Hubbard, T., Kujath, M., 2006, “Theoretical and experimental analysis of an off-chip microgripper,” Canadian Journal of Electrical and Computer Engineering, Vol. 31, No. 2. These devices rely on localized changes in temperature for actuation. A few of these studies are summarized below.
Wang et al. describe the architecture of a three-probe MEMS nanomanipulator with nano-scale end effectors. See, Wang, X, Vincent, L., Yu, M., Huang, Y., Liu, c., 2003, “Architecture of a Three-Probe MEMS Nanomanipulator with Nanoscale End-Effectors,” Proceedings of the 2003 IEEE/ASME International Conference on Advanced Intelligent Mechatronics. Micromachining and nanofabrication techniques are employed in the fabrication of this device. Unlike the micro-tweezers discussed before which can manipulate objects in the micron range, this device shown in FIG. 1e is capable of picking up nano-scale objects such as carbon nanotube structures having an average diameter of 1 nm. Each probe beam is 300 μm long with nano end-effectors. The actuation is achieved by increasing the temperature at the interface of the “actuator” metal and the silicon nitride cantilever, by means of a voltage application. Due to unequal expansion of the silicon nitride and silicon, the cantilever displaces from its position as shown in FIG. 1e. 
Another thermally actuated device was developed by Nguyen et al. See, Nguyen, N., Ro, S., Low, Lee-Ngo, C., 2004, “A polymeric microgripper with integrated thermal actuators,” Journal of Micromechanics and Microengineering, Vol. 14, pp. 969-974. This micro-tweezers was fabricated using a polymeric surface micromachining process, which utilized 100 μm thick SU-8 deposited and patterned over silicon. A stencil wafer was fabricated using deep reactive ion etching to define heating pads. Another thermally actuated micro gripper was developed by Ivanova et al. that was fabricated from single crystal bulk silicon. See, Ivanova, K., Ivanov, T., Badar, A., Volland, B. E., 2006, “Thermally driven microgripper as a tool for micro assembly,” Microelectronic Engineering, Vol. 83, pp. 1393-1395. The gripper employs thermally grown oxide as an insulating layer on a single crystal silicon substrate with a layer of (Cr/Au) deposited on top of the oxide. Current passes through hot arms of the device to cause Joule heating. A cold arm is shorter and wider than the hot arm hence so that the short arm does not heat up at the same rate. This difference in heating causes a torque at the tips which closes the device. Chronis et al. developed another SU-8-based, thermally actuated micro-tweezers that uses a similar hot and cold arm arrangement. See, Chronis, N, Lee, L. P., 2005, “Electrothermally Activated SU-8 Microgripper for Single Cell Manipulation in Solution,” Journal of Microelectromechanical systems, Vol. 14, No. 4, pp. 857-863.
Researchers have also developed micro-grippers based on electrostatic actuation. See e.g., Millet, O., Bemardoni, P., Régnier, S., Bidaud, P., 2004, “Electrostatic actuated micro gripper using an amplification mechanism,” Sensors and Actuators, Vol. 114, pp. 371-378; Kim, Chang-Jin, Pisano, A. P., Muller, R. S., 1992, “Silicon-Processed Overhanging Microgripper,” Journal of Microelectromechanical Systems, Vol. I, No. I; Neild, A., Oberti, S., Beyeler, F., Dual, J., Nelson, B. J., 2006, “A micro-particle positioning technique combining an ultrasonic manipulator and a microgripper,” Journal of Micromechanics and Microengineering, Vol. 16, pp. 1562-1570; Almeida, V. A. L. de., 2004, “Microgrippers Driven by Electrostatic Comb Drive Actuators,” ABCM Symposium series in Mechatronics, Vol. 1, pp. 682-687; and Volland, B. E., 2002, “Electrostatically driven microgripper,” Microelectronic Engineering, Vol. 61, pp. 1015-1023. Volland et al. fabricated an electrostatically actuated micro-gripper using silicon-on-insulator wafers. See, Volland, B. E., Heerlein, H., Rangelow, L W., 2002, “Electrostatically driven microgripper,” Microelectronic Engineering, Vol. 61, pp. 1015-1023. The gripper, depicted in FIG. 1f has an electrostatically driven micro-actuator which generates a linear motion that is converted to rotational (gripping) motion by a hinge system. The tweezers opening is 170 μm while the length of the tweezers prongs is 1 mm. The actuation mechanism for this device is shown in the detail view of FIG. 1g. 
Electro-static actuators are less frequently employed in micro-gripper devices than piezoelectric or electro-thermal actuators. One reason is their inherent limitation of operation in liquid. Comb drives which are the driving forces for most electrostatic actuators require an intricate and complex fabrication process. These drives are susceptible to dust contamination and comb misalignment and failure. Like piezoelectric and thermally-actuated devices, they also cannot act as standalone devices due to their external power requirement.
Another actuation method studied to a lesser extent in micro-gripping systems is pneumatic actuation. Pneumatically actuated devices make use of fluid pressure for mechanical actuation of gripper structures. See e.g., Butefisch, S., 2002, “Novel Micro-pneumatic actuator for MEMS,” Sensors and Actuators, Vol. 97, pp. 638-645. In devices of this type, pressure applied through the capillary tubes to spring elements moves pistons, which actuate the gripper tips via intricately fabricated hinges Pneumatically actuated grippers suffer from some drawbacks, the biggest being the need for external equipment to provide the fluid pressure to actuate the mechanism. This poses an additional complexity in the fabrication which increases the cost of the device and reduces its reproducibility. In addition, the device can be incapacitated with a slight defect in the sealing. In such an event, the small geometry of this device can significantly hinder the troubleshooting.
Most of the prior micromanipulation device or micro-tweezers involve a large number of complex fabrication steps that not only add to the cost of the device but quite often render it too impractical to fabricate and/or use. Unlike fabrication of most macro-scale objects, a flaw in microfabrication can rarely be fixed without starting over. Furthermore, the actuation mechanisms of all existing systems require external power consumption which not only adds to operation costs but also requires additional instrumentation, such as power supplies and amplifiers. The overall complexity of these devices (both in fabrication, instrumentation and operation) has hampered the development and use of these devices so that they are not widely used in any industry.
There is a need for a micromanipulation device for grasping and manipulating micro-sized objects that can be easily manufactured on a micro-scale and that can be operated without the need for additional instrumentation.